Alkoxysilane/organic polymer composition for thin insulating film production and use thereof

ABSTRACT

Disclosed is an alkoxysilane/organic polymer composition for use in producing an insulating thin film, comprising (A) a specific alkoxysilane; (B) a specific organic polymer; and (C) a solvent for alkoxysilane (A) and organic polymer (B), wherein solvent (C) comprises at least one organic solvent selected from the group consisting of amide linkage-containing organic solvents and ester linkage-containing organic solvents. Also disclosed are a silica-organic polymer composite thin film which is produced by a process comprising: forming a thin film of the composition of the present invention; subjecting the thin film to a hydrolysis and dehydration-condensation reaction with respect to the alkoxysilane thereof, to thereby cause the alkoxysilane to be gelled in the thin film; and removing the solvent remaining in the thin film by drying, and a porous silica thin film which is obtained by removing the organic polymer from the silica-organic polymer composite thin film. Both of the silica-organic polymer composite thin film and the porous silica thin film have advantages not only in that these thin films have a low dielectric constant suitable for insulating layers for a multilevel interconnect for a semiconductor device, but also in that these thin films can be produced by a method which can be easily performed in the current process for producing a semiconductor device.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP98/03186 which has an Internationalfiling date of Jul. 15, 1998, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alkoxysilane/organic polymercomposition for use in producing an insulating thin film.

More particularly, the present invention is concerned with analkoxysilane/organic polymer composition for use in producing aninsulating thin film, comprising (A) a specific alkoxysilane; (B) aspecific organic polymer; and (C) a solvent for alkoxysilane (A) andorganic polymer (B), wherein the solvent (C) comprises at least oneorganic solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents. In a current process for producing a semiconductor device, asilicon oxide insulating layer is produced by a method comprisingdissolving a silicon oxide precursor in an appropriate solvent tothereby obtain a solution of the silicon oxide precursor, forming acoating of the obtained solution on a substrate by spin coatingtechnique or the like, and calcining the coating at an appropriatetemperature. When the composition of the present invention is used as amaterial for an insulating layer in the production of a multilevelinterconnect for a semiconductor device, an insulating layer having alow dielectric constant can be produced by a method which can be easilyperformed in the current process for producing a semiconductor device.The present invention is also concerned with a multilevel interconnectfor a semiconductor device, which comprises a plurality of insulatinglayers and circuits formed on the insulating layers, wherein at leastone layer of the insulating layers is obtained using the above-mentionedcomposition. Further, the present invention is concerned with asemiconductor device comprising the above-mentioned multilevelinterconnect.

2. Background Art

Conventionally, as a material for an insulating layer for a multilevelinterconnect for a semiconductor device, such as an LSI, silica (havinga dielectric constant of from 4.0 to 4.5) or the like has generally beenused. In recent years, the density of the circuit of a semiconductordevice (such as an LSI) has become higher and higher, and, hence, thedistance between mutually adjacent conducting lines in the circuit hasbecome extremely small. As a consequence of this, the mutually adjacentconducting lines having insulators therebetween have inadvertently cometo function as a condenser. This has posed a problem that, when thedielectric constant of the insulator is high, the electrostatic capacityof the condenser inadvertently formed by the mutually adjacentconducting lines and the insulators present therebetween becomes high,so that the transmission of the electric signals through each of themutually adjacent conducting lines is markedly delayed. In order tosolve this problem, with respect to a material for an insulating layerfor a multilevel interconnect, studies have been made to develop amaterial having a much lower dielectric constant.

It is known that, among conventional materials, polytetrafluoroethylenehas a lowest dielectric constant, which is approximately 1.9. However,in general, fluororesins have a problem in that fluororesins have notonly poor adhesion to a substrate and a circuit but also poor heatresistances. Further, in recent years, the dielectric constant of aninsulating layer is required to be less than 1.9.

On the other hand, attempts have been made in which the dielectricconstant of a conventional material is decreased by rendering thematerial porous, thereby providing a porous material which is acomposite comprised of the conventional material and air (having adielectric constant of 1.0).

A silica aerogel (which is a type of porous silica) is a representativeexample of such porous materials. However, production of a silicaaerogel requires supercritical drying. Therefore, production of a silicaaerogel requires not only a long time, but also extremely complicatedsteps of operations using a specially designed apparatus, so that it ispractically impossible to introduce a step for producing a silicaaerogel insulating layer into the current process for producing asemiconductor device.

U.S. Pat. No. 5,472,913 discloses a method for producing a porous silicaby a special technique requiring no supercritical drying. However, thismethod still requires extremely complicated steps of operations, so thatit is difficult to introduce a step in which a porous silica insulatinglayer is produced by this method into the current process for producinga semiconductor device.

Journal of Macromolecular Science-Chemistry, A27, 13-14 p.1603 (1990)discloses a method for producing a porous silica, which comprisessubjecting an alkoxysilane to a hydrolysis and dehydration-condensationreaction in the presence of a specific organic polymer so as to cause agelation of the alkoxysilane, thereby obtaining a homogeneousorganic-inorganic composite comprised of the organic polymer and silica,and heating the obtained composite for calcination so that the organicpolymer in the composite can be thermally decomposed and removed,thereby obtaining a porous silica. However, in this method, thecalcination for completely decomposing and removing the organic polymeris required to be conducted in an atmosphere of air at a temperature ashigh as 600° C. or more, so that it is impossible to introduce a step inwhich a porous silica insulating layer is produced by this method intothe current process for producing a semiconductor device.

Further, as described below, methods for producing a porous thin film orthe like, which are similar to the above-mentioned method disclosed inJournal of Macromolecular Science-Chemistry, are disclosed in UnexaminedJapanese Patent Application Laid-Open Specification Nos. 8-245278 and7-100389 and WO97/06896.

Unexamined Japanese Patent Application Laid-Open Specification No.8-245278 discloses a method for producing a porous ceramic thin film,which comprises coating a substrate with an alcohol solution of a metalalkoxide, which solution contains polyethylene glycol added thereto, andcalcining the resultant coating.

Unexamined Japanese Patent Application Laid-Open Specification No.7-100389 discloses a method for producing a carrier for a catalyst foruse in petroleum refining, which comprises subjecting a metal alkoxideto a hydrolysis and dehydration-condensation reaction in the presence ofan organic polymer, and calcining the resultant product.

WO97/06896 discloses a method for producing a porous metal oxide film,which comprises dissolving a metal alkoxide, an acid and an organicpolymer in a mixed solvent of a first solvent and water to therebyobtain a coating solution, coating the obtained solution onto a glasssubstrate to form a gel film on the substrate, drying the gel film,immersing the dried gel film in a second solvent to extract and removethe organic polymer from the gel film, and calcining the gel film tothereby obtain a porous metal oxide film.

It is noted that, in each of the methods disclosed in UnexaminedJapanese Patent Application Laid-Open Specification Nos. 8-245278 and7-100389 and WO97/06896, an alcohol is used as a solvent for each of themetal alkoxide and the organic polymer. For the reason as describedbelow, the use of an alcohol as a solvent disadvantageously causes alowering of the void ratio of an obtained porous material, therebymaking it impossible to obtain such a porous insulating thin film havinga low dielectric constant as can be suitably used in a multilevelinterconnect for a semiconductor device.

As is apparent from the above, such an insulating thin film having a lowdielectric constant as can be suitably used in a multilevel interconnectfor a semiconductor device has conventionally been unable to be producedby a method which can be easily performed in the current process forproducing a semiconductor device.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward developing an insulating thin filmfor use in a multilevel interconnect for a semiconductor device, whereinthe insulating thin film not only has a low dielectric constant, butalso can be produced by a method which can be easily performed in thecurrent process for producing a semiconductor device. As a result, ithas unexpectedly been found that the above objective can be attained byusing an alkoxysilane/organic polymer composition comprising (A) aspecific alkoxysilane; (B) a specific organic polymer; and (C) a solventfor alkoxysilane (A) and organic polymer (B), wherein the solvent (C)comprises at least one organic solvent selected from the groupconsisting of amide linkage-containing organic solvents and esterlinkage-containing organic solvents. More specifically, it hasunexpectedly been found that an insulating thin film produced from theabove alkoxysilane/organic polymer composition not only has a lowdielectric constant which is suitable for an insulating layer for amultilevel interconnect for a semiconductor device, but also can beproduced by a method which can be easily performed in the currentprocess for producing a semiconductor device, wherein the insulatingthin film is either a silica-organic polymer composite thin film(produced by forming a thin film from the above alkoxysilane/organicpolymer composition and then subjecting the thin film to heat treatment)or a porous silica thin film (obtained by removing the organic polymerfrom the silica-organic polymer composite thin film). The presentinvention has been completed, based on the above novel finding.

Therefore, it is a primary object of the present invention to provide acomposition for use in producing an insulating layer for a multilevelinterconnect for a semiconductor device, wherein the insulating layernot only has a low dielectric constant, but also can be produced by amethod which can be easily performed in the current process forproducing a semiconductor device.

It is another object of the present invention to provide a compositeinsulating thin film which can be produced from the above-mentionedcomposition, and a porous silica thin film which can be obtained fromthe above composite insulating thin film, as well as the uses of thesethin films.

The foregoing and other objects, features and advantages of the presentinvention will be apparent to those skilled in the art from thefollowing detailed description and appending claims.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided analkoxysilane/organic polymer composition for use in producing aninsulating thin film, comprising:

(A) at least one alkoxysilane selected from the group consisting of (1)tetraalkoxysilanes, (2) trialkoxysilanes, (3) dialkoxysilanes, (4)monoalkoxysilanes and (5) trialkoxysilane dimers, respectively,represented by the following formulae (1), (2), (3), (4) and (5):

Si(OR)₄  (1),

R¹Si(OR)₃  (2),

R¹R²Si(OR)₂  (3),

R¹R²R³SiOR  (4),

and

(RO)₃Si—R⁴—Si(OR)₃  (5),

wherein each R independently represents a straight chain or branchedalkyl group having 1 to 6 carbon atoms, each of R¹, R² and R³independently represents a hydrogen atom or a monovalent hydrocarbongroup having 1 to 6 carbon atoms, and R⁴ represents a divalenthydrocarbon group having 1 to 6 carbon atoms, and wherein, when thealkoxysilane (A) is at least one first alkoxysilane selected from thegroup consisting of the alkoxysilanes (3) and (4), the firstalkoxysilane is used in combination with at least one secondalkoxysilane selected from the group consisting of the alkoxysilanes(1), (2) and (5);

(B) at least one organic polymer having a main chain mainly comprisingat least one polymer chain selected from the group consisting of analiphatic polyether chain having ether group-containing recurring unitshaving 2 to 12 carbon atoms, an aliphatic polyester chain having estergroup-containing recurring units having 2 to 12 carbon atoms, analiphatic polycarbonate chain having carbonate group-containingrecurring units having 2 to 12 carbon atoms and an aliphaticpolyanhydride chain having anhydride group-containing recurring unitshaving 2 to 12 carbon atoms; and

(C) a solvent for the alkoxysilane (A) and the organic polymer (B),wherein the solvent (C) comprises at least one organic solvent selectedfrom the group consisting of amide linkage-containing organic solventsand ester linkage-containing organic solvents,

and wherein at least a part of the alkoxysilane (A), which is at leastone alkoxysilane selected from the group consisting of the alkoxysilanes(1) to (5), is optionally in at least one form selected from the groupconsisting of an oligomer form and an at least partially hydrolyzedform.

For easy understanding of the present invention, the essential featuresand various embodiments of the present invention are enumerated below.

1. An alkoxysilane/organic polymer composition for use in producing aninsulating thin film, comprising:

(A) at least one alkoxysilane selected from the group consisting of (1)tetraalkoxysilanes, (2) trialkoxysilanes, (3) dialkoxysilanes, (4)monoalkoxysilanes and (5) trialkoxysilane dimers, respectively,represented by the following formulae (1), (2), (3), (4) and (5):

 Si(OR)₄  (1),

R¹Si(OR)₃  (2),

R¹R²Si(OR)₂  (3),

R¹R²R³SiOR  (4),

and

(RO)₃Si—R⁴—Si(OR)₃  (5),

wherein each R independently represents a straight chain or branchedalkyl group having 1 to 6 carbon atoms, each of R¹, R² and R³independently represents a hydrogen atom or a monovalent hydrocarbongroup having 1 to 6 carbon atoms, and R⁴ represents a divalenthydrocarbon group having 1 to 6 carbon atoms, and wherein, when thealkoxysilane (A) is at least one first alkoxysilane selected from thegroup consisting of the alkoxysilanes (3) and (4), the firstalkoxysilane is used in combination with at least one secondalkoxysilane selected from the group consisting of the alkoxysilanes(1), (2) and (5);

(B) at least one organic polymer having a main chain mainly comprisingat least one polymer chain selected from the group consisting of analiphatic polyether chain having ether group-containing recurring unitshaving 2 to 12 carbon atoms, an aliphatic polyester chain having estergroup-containing recurring units having 2 to 12 carbon atoms, analiphatic polycarbonate chain having carbonate group-containingrecurring units having 2 to 12 carbon atoms and an aliphaticpolyanhydride chain having anhydride group-containing recurring unitshaving 2 to 12 carbon atoms; and

(C) a solvent for the alkoxysilane (A) and the organic polymer (B),wherein the solvent (C) comprises at least one organic solvent selectedfrom the group consisting of amide linkage-containing organic solventsand ester linkage-containing organic solvents,

and wherein at least a part of the alkoxysilane (A), which is at leastone alkoxysilane selected from the group consisting of the alkoxysilanes(1) to (5), is optionally in at least one form selected from the groupconsisting of an oligomer form and an at least partially hydrolyzedform.

2. The composition according to item 1 above, wherein the alkoxysilane(A) is a mixture of at least one tetraalkoxysilane (1) and at least onealkoxysilane selected from the group consisting of the alkoxysilanes (2)to (5).

3. The composition according to item 1 above, wherein the alkoxysilane(A) is at least one trialkoxysilane (2), or a mixture of at least onetrialkoxysilane (2) and at least one alkoxysilane selected from thegroup consisting of the alkoxysilanes (1) and (3) to (5).

4. The composition according to any one of items 1 to 3 above, whereinthe solvent (C) further comprises at least one alcohol.

5. The composition according to any one of items 1 to 4 above, whichfurther comprises (D) at least one acid capable of functioning as acatalyst for promoting a hydrolysis and dehydration-condensationreaction of the alkoxysilane (A).

6. The composition according to any one of items 1 to 5 above, whereinthe organic polymer (B) is an aliphatic polyether comprising apolyalkylene glycol having C₂-C₁₂ ether group-containing recurring unitsand having a number average molecular weight of from 200 to 1,000,000.

7. The composition according to any one of items 1 to 6 above, whereinthe organic polymer (B) is present in an amount of from 0.1 to 10 interms of a weight ratio relative to the amount of a product obtained bysubjecting the entire amount of the alkoxysilane (A) to a hydrolysis anddehydration-condensation reaction.

8. A silica-organic polymer composite thin film, which is produced by aprocess comprising:

forming a thin film of the composition of any one of items 1 to 7 above;

subjecting the thin film to a hydrolysis and dehydration-condensationreaction with respect to the alkoxysilane (A) thereof, to thereby causethe alkoxysilane (A) to be gelled in the thin film; and

removing the solvent (C) remaining in the thin film by drying.

9. The silica-organic polymer composite thin film according to item 8above, which has a thickness of from 0.1 to 100 μm.

10. The silica-organic polymer composite thin film according to item 8or 9 above, which is transparent to visible rays having a wavelength offrom 0.4 to 0.7 μm.

11. A multilevel interconnect comprising a plurality of insulatinglayers and circuits formed on the insulating layers, wherein at leastone layer of the insulating layers comprises the silica-organic polymercomposite thin film of any one of items 8 to 10 above.

12. A semiconductor device comprising the multilevel interconnect ofitem 11 above.

13. A porous silica thin film which is obtained by removing the organicpolymer from the silica-organic polymer composite thin,film of any oneof items 8 to 10 above.

14. The porous silica thin film according to item 13 above, which has anaverage pore diameter of from 1 to 500 nm.

15. The porous silica thin film according to item 13 or 14 above,wherein the removal of the organic polymer from the silica-organicpolymer composite thin film is performed by calcining the composite thinfilm at a temperature of not higher than 450° C.

16. The porous silica thin film according to any one of items 13 to 15above, which has a surface thereof treated with a silylating agent.

17. A multilevel interconnect comprising a plurality of insulatinglayers and circuits formed on the insulating layers, wherein at leastone layer of the insulating layers comprises the porous silica thin filmof any one of items 13 to 16 above.

18. A semiconductor device comprising the multilevel interconnect ofitem 17 above.

Hereinbelow, the present invention will be described in detail.

At least one alkoxysilane which is used as component (A) of thealkoxysilane/organic polymer composition of the present invention isselected from the group consisting of (1) tetraalkoxysilanes, (2)trialkoxysilanes, (3) dialkoxysilanes, (4) monoalkoxysilanes and (5)trialkoxysilane dimers, respectively, represented by the followingformulae (1) to (5):

Si(OR)₄  (1),

R¹Si(OR)₃  (2),

R¹R²Si(OR)₂  (3),

R¹R²R³SiOR  (4),

and

(RO)₃Si—R⁴—Si(OR)₃  (5),

wherein each R independently represents a straight chain or branchedalkyl group having 1 to 6 carbon atoms, each of R¹, R² and R³independently represents a hydrogen atom or a monovalent hydrocarbongroup having 1 to 6 carbon atoms, and R⁴ represents a divalenthydrocarbon group having 1 to 6 carbon atoms. Examples of alkyl groupswhich can be suitably used as R in formulae (1), (2), (3), (4) and (5)above include a methyl group, an ethyl group, an n-propyl group, ani-propyl group, an n-butyl group, an i-butyl group and a t-butyl group.Examples of monovalent hydrocarbon groups which can be suitably used asR¹, R² and R³ in formulae (2), (3) and (4) above include a methyl groupand a phenyl group. Further, examples of divalent hydrocarbon groupswhich can be suitably used as R⁴ in formula (5) above include amethylene group, an ethylene group, an isopropylidene group and aphenylene group.

It is preferred that the alkoxysilane (A) comprises at least onealkoxysilane selected from the group consisting of alkoxysilanes (1),(2) and (5), to which, if desired, at least one alkoxysilane selectedfrom the group consisting of alkoxysilanes (3) and (4) is added.

It is especially preferred that the alkoxysilane (A) is:

1) a mixture of at least one of the above-mentioned alkoxysilane (1) andat least one alkoxysilane selected from the group consisting of theabove-mentioned alkoxysilanes (2) to (5);

2) at least one of the above-mentioned trialkoxysilane (2); or

3) a mixture of at least one of the above-mentioned trialkoxysilane (2)and at least one alkoxysilane selected from the group consisting of theabove-mentioned alkoxysilanes (1) and (3) to (5).

When the alkoxysilane (A) is at least one first alkoxysilane selectedfrom the group consisting of the alkoxysilanes (3) and (4), the firstalkoxysilane is used in combination with at least one secondalkoxysilane selected from the group consisting of alkoxysilanes (1),(2) and (5).

When the alkoxysilane (A) is only at least one alkoxysilane selectedfrom the group consisting of the alkoxysilanes (3) and (4), thealkoxysilane (A) cannot be gelled by a method in which a thin filmobtained from the composition of the present invention for use inproducing an insulating thin film is subjected to a hydrolysis anddehydration-condensation reaction with respect to the alkoxysilane (A)thereof. Therefore, in such a case, any of the silica-organic polymercomposite thin film and porous silica thin film of the present inventiondescribed below cannot be obtained.

In the above-mentioned preferred form 1) of the alkoxysilane (A), whenthe amount of the at least one alkoxysilane selected from the groupconsisting of the above-mentioned alkoxysilanes (2) to (5) is reducedand the amount of the above-mentioned tetraalkoxysilane (1) isincreased, the crosslinking density of the product obtained by thehydrolysis and dehydration-condensation reaction of the above-mentionedalkoxysilane (A) is increased, so that the mechanical strength of thesilica-organic polymer composite thin film and porous silica thin filmof the present invention described below is improved.

On the other hand, in the above-mentioned preferred form 1) of thealkoxysilane (A), when the amount of the above-mentionedtetraalkoxysilane (1) is reduced and the amount of the at least onealkoxysilane selected from the group consisting of the above-mentionedalkoxysilanes (2) to (5) is increased, the crosslinking density of theproduct obtained by the hydrolysis and dehydration-condensation reactionof the above-mentioned alkoxysilane (A) is lowered, so that the producthas an improved cracking resistance. Further, when the hydrocarbongroups are directly bonded to the silicon atoms, the hygroscopicity ofthe above-mentioned reaction product is extremely reduced by theinfluence of the hydrocarbon groups.

At least a part of the alkoxysilane (A), which is at least onealkoxysilane selected from the group consisting of the above-mentionedalkoxysilanes (1) to (5), is optionally in the form of an oligomer, andat least a part of the alkoxysilane (A), which is at least onealkoxysilane selected from the group consisting of the above-mentionedalkoxysilanes (1) to (5), is optionally in or at least partiallyhydrolyzed form. Further, metal alkoxides which can be condensed withthe above-mentioned alkoxysilanes (1) to (5) may be optionally added tothe above-mentioned alkoxysilanes (1) to (5). Examples of such optionalmetal alkoxides include C₁-C₆ alkoxides of aluminum, titanium,zirconium, boron, magnesium, germanium, zinc, tin, niobium, lead,strontium, lithium and barium. Among these, C₁-C₆ alkoxides of aluminum,titanium and zirconium are preferred. The amount of the optional metalalkoxide is preferably 30% by weight or less, based on the weight of thealkoxysilane (A).

Specific examples of alkoxysilanes which can be used as theabove-mentioned alkoxysilanes (1) to (5) include tetramethoxysilane,tetraethoxysilane, tetra(n-propoxy)silane, tetra(i-propoxy)silane,tetra(n-butoxy)silane, tetra(t-butoxy)silane, trimethoxysilane,triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane,phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane,dimethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane,phenyldimethoxysilane, phenyldiethoxysilane, methyldimethoxysilane,methyldiethoxysilane, phenylmethyldimethoxysilane,phenylmethyldiethoxysilane, trimethylmethoxysilane,trimethylethoxysilane, triphenylmethoxysilane, triphenylethoxysilane,phenyldimethylmethoxysilane, phenyldimethylethoxysilane,diphenylmethylmethoxysilane, diphenylmethylethoxysilane,dimethylmethoxysilane, dimethylethoxysilane, diphenylmethoxysilane,diphenylethoxysilane, bis(trimethoxysilyl)methane,bis(triethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane,1,2-bis(triethoxysilyl)ethane, 1,4-bis(trimethoxysilyl)benzene and1,4-bis(triethoxysilyl)benzene. Among these, especially preferred aretetramethoxysilane, tetraethoxysilane, trimethoxysilane,triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane,dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilaneand trimethylethoxysilane.

As is apparent from the below-mentioned specific examples of organicpolymers usable as component (B), the organic polymer (B) of thealkoxysilane-organic polymer composition of the present inventioncomprises at least one organic polymer having a main chain mainlycomprising at least one polymer chain selected from the group consistingof an aliphatic polyether chain having ether group-containing recurringunits having 2 to 12 carbon atoms, an aliphatic polyester chain havingester group-containing recurring units having 2 to 12 carbon atoms, analiphatic polycarbonate chain having carbonate group-containingrecurring units having 2 to 12 carbon atoms and an aliphaticpolyanhydride chain having anhydride group-containing recurring unitshaving 2 to 12 carbon atoms.

The organic polymer (B) may be a single polymer or a mixture of aplurality of polymers. As long as the effect of the present invention isnot adversely affected, the organic polymer (B) may optionally comprisea polymer chain having recurring units other than the above-mentionedrecurring units. Further, the main chain of the organic polymer (B) mayoptionally have a functional group at terminals thereof. Usually, in apolyether, a polyester, a polycarbonate and a polyanhydride, theterminal groups are comprised of a hydroxyl group and/or a carboxylgroup. However, the terminal groups of the main chain of the organicpolymer (B) are not particularly limited to hydroxyl and carboxylgroups. As long as the effect of the present invention is not adverselyaffected, the terminal groups of the main chain of the organic polymer(B) may optionally be modified with other functional groups.

Examples of aliphatic polyethers having ether group-containing recurringunits having 2 to 12 carbon atoms include polyalkylene glycols, such aspolyethylene glycol, polypropylene glycol, polytrimethylene glycol,polytetramethylene glycol, polypentamethylene glycol, polyhexamethyleneglycol, polydioxolane, polydioxepane and the like.

Examples of aliphatic polyesters having ester group-containing recurringunits having 2 to 12 carbon atoms include polycondensation products of ahydroxycarboxylic acid and ring-opening polymerization reaction productsof a lactone, such as polyglycolide, polycaprolactone,polycaprolactonetriol, polypivalolactone and the like; andpolycondensation products of a dicarboxylic acid with an alkyleneglycol, and ring-opening copolymerization products of an epoxide with anacid anhydride, such as polyethylene oxalate, polyethylene succinate,polyethylene adipate, polyethylene suberate, polyethylene sebacate,polypropylene adipate, polyoxydiethylene malonate, polyoxydiethyleneadipate and the like.

Examples of aliphatic polycarbonates having carbonate group-containingrecurring units having 2 to 12 carbon atoms include polycondensationreaction products of carbonic acid and alkylene glycols, such aspolyethylene carbonate, polypropylene carbonate, polytrimethylenecarbonate, polytetramethylene carbonate, polypentamethylene carbonate,polyhexamethylene carbonate and the like.

Examples of aliphatic polyanhydrides having anhydride group-containingrecurring units having 2 to 12 carbon atoms include polycondensationreaction products of dicarboxylic acids, such as polymalonyl oxide,polyadipoyl oxide, polypimeloyl oxide, polysuberoyl oxide, polyazelaoyloxide, polysebacoyl oxide and the like.

Of these, especially preferred are polyethylene glycol, polypropyleneglycol, polycaprolactone, polycaprolactonetriol, polyethylene carbonate,polypentamethylene carbonate, polyhexamethylene carbonate, polyadipoyloxide, polyazelaoyl oxide and polysebacoyl oxide.

The term “alkylene glycol” means a dihydric alcohol obtained bysubstituting an alkane having two or more carbon atoms with two hydroxylgroups so that two hydrogen atoms bonded to different carbon atoms inthe alkane are replaced by the hydroxyl groups. The term “dicarboxylicacid” means an organic acid having two carboxyl groups, such as oxalicacid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelicacid, suberic acid, azelaic acid, sebacic acid or the like.

When either aliphatic polymers other than the above-mentioned aliphaticpolymers or aromatic polymers are used as organic polymer (B), problemsarise in that the homogeneity of the silica-organic polymer compositethin film becomes poor and the required calcination temperature becomeshigh, thus rendering it difficult to produce any of the silica-organicpolymer composite thin film and porous silica thin film of the presentinvention in the current process for producing a semiconductor device.However, for the purpose of adjusting the viscosity of the compositionor improving the coating properties of the composition, other optionalpolymers may be used in addition to organic polymer (B) defined in thepresent invention, as long as the desired effects of the presentinvention are not impaired.

The amount of the organic polymer (B) in the composition of the presentinvention varies depending on the physical properties desired for thesilica-organic polymer composite thin film or the porous silica thinfilm. Generally, the amount of the organic polymer (B) is 10⁻² to 100,preferably 10⁻¹ to 10, more preferably 0.5 to 5, in terms of a weightratio relative to the amount of a product obtained by subjecting theentire amount of the alkoxysilane (A) to a hydrolysis anddehydration-condensation reaction. When the above-defined weight ratioof the organic polymer (B) is less than 10³¹ ², problems arise in that alarge-thickness coating of the composition cannot be obtained, that agood silica-organic polymer composite thin film having a satisfactorycrack resistance cannot be obtained, and that a porous silica thin filmhaving a satisfactory void ratio cannot be obtained. On the other hand,when the above-defined weight ratio of the organic polymer (B) is largerthan 100, problems arise in that any of the silica-organic polymercomposite thin film and the porous silica thin film cannot have asatisfactory mechanical strength.

It is preferred that the organic polymer (B) has a number averagemolecular weight of from 200 to 1,000,000. It should be noted that thepore size of the porous silica thin film of the present invention isvery small and has only a small dependency on the molecular weight ofthe organic polymer (B). This is a great difference between the presentinvention and the conventional technique, and such difference is one ofthe reasons why the composite thin film and porous silica thin film ofthe present invention are especially excellent as insulating layers fora multilevel interconnect for a semiconductor device.

In the alkoxysilane/organic polymer composition of the presentinvention, it is required that the solvent (C) for the alkoxysilane (A)and the organic polymer (B) comprise at least one organic solventselected from the group consisting of amide linkage-containing organicsolvents and ester linkage-containing organic solvents. If such asolvent is not used, a gelation of the alkoxysilane (A) by thehydrolysis and dehydration-condensation reaction of the alkoxysilane (A)does not proceed efficiently, leading to a problem that, when theorganic polymer (B) is removed from the silica-organic polymer compositethin film, the silica-organic polymer composite thin film shrinks,thereby making it impossible to obtain a porous silica thin film havinga high void ratio and hence a low dielectric constant. This is thereason why a porous film having a high void ratio cannot be obtained bythe techniques disclosed in the above-mentioned Unexamined JapanesePatent Application Laid-Open Specification Nos. 8-245278 and 7-100389and WO97/06896.

The solvent (C) used in the present invention, i.e., at least oneorganic solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents exhibits the effect to suppress an aggregation of the dispersedmolecular chains of the organic polymer (B) in the silica-organicpolymer composite film, thereby suppressing the growth of the polymerphase toward large particles. Generally, the interaction between silicaand the organic polymer (B) used in the present invention is not strong.Therefore, if at least one organic solvent selected from the groupconsisting of amide linkage-containing organic solvents and esterlinkage-containing organic solvents is not used as the solvent (C), aproblem arises that, during the course of the gelation of thealkoxysilane (A) in the production of the silica-organic polymercomposite thin film, an aggregation of the molecular chains of theorganic polymer (B) occurs, thereby forming large particles of theorganic polymer (B) in the obtained silica-organic polymer compositethin film. If a porous silica thin film is produced from asilica-organic polymer composite thin film containing such largeparticles of the organic polymer (B), the removal of the organic polymer(B) causes the formation of large pores in the porous silica thin film,wherein the large pores are likely to adversely affect the multilevelinterconnect used as a semiconductor device.

The formation of a thin film is performed by coating a substrate withthe composition of the present invention. As a method for forming a thinfilm, any conventional method, such as casting, immersing, spin coatingand the like, can be employed. However, the spin coating method issuitable when the production of the insulating layer is intended in acurrent process for producing a multilevel interconnect for asemiconductor device. The thickness of the thin film can be controlledwithin the range of from 0.1 μm to 100 μm by varying the viscosity ofthe composition and the revolution rate of the spin coater. When thethickness of the thin film is larger than 100 μm, the thin film tends tosuffer cracking. Generally, when the insulating layer is used in amultilevel interconnect for a semiconductor device, the suitablethickness of the insulating layer is 0.5 μm to 5 μm.

With respect to the solvent (C), it is preferred that the amount of atleast one organic solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents in the solvent (C) is 1% by weight or more, based on the totalweight of the solvent (C). If the amount of the above-mentioned at leastone organic solvent is less than 1% by weight, based on the total weightof the solvent (C), an aggregation of the molecular chains of theorganic polymer (B) occurs, thereby forming large particles of theorganic polymer (B) in the silica-organic polymer composite thin film,so that a problem tends to arise that a porous silica thin film having asmall pore size and a high void ratio cannot be obtained.

Examples of amide linkage-containing solvents usable in the presentinvention include amides, such as formamide, N-methylformamide,N-ethylformamide, N,N-dimethylformamide, N,N-diethylformamide,N-methylacetamide, N-ethylacetamide, N,N-dimethylacetamide,N,N-diethylacetamide, N-methylpyrrolidone, N-formylmorpholine,N-acetylmorpholine, N-formylpiperidine, N-acetylpiperidine,N-formylpyrrolidine, N-acethylpyrrolidine, N,N′-diformylpiperadine,N,N′-diacethylpiperadine and the like, and ureas, such astetramethylurea, N,N′-dimethylimidazolidinone and the like. Examples ofester linkage-containing solvents usable in the present inventioninclude ethyl formate, methyl acetate, ethyl acetate, ethyl lactate,ethylene glycol monomethyl ether acetate, ethylene glycol diacetate,propylene glycol monomethyl ether acetate, diethyl carbonate, ethylenecarbonate, propylene carbonate and the like. Of these, particularlypreferred are N,N-dimethylformamide, N,N-dimethylacetamide,N-methylpyrrolidone, tetramethylurea, N,N′-dimethylimidazolidinone,ethylene glycol monomethyl ether acetate, ethylene glycol diacetate andpropylene glycol monomethyl ether acetate.

One solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents may be used alone as the solvent (C). However, when either amixed solvent of at least two different organic solvents selected fromthe group consisting of amide linkage-containing organic solvents andester linkage-containing organic solvents or a mixed solvent of at leastone organic solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents and at least one organic solvent other than the amidelinkage-containing and ester linkage-containing organic solvents is usedas the solvent (C), advantages can be obtained in that the viscosity ofthe composition and the evaporation rate of the solvent (C) can beeasily controlled. Preferred examples of other organic solvents whichcan be employed in combination with at least one organic solventselected from the group consisting of amide linkage-containing organicsolvents and ester linkage-containing organic solvents include alcohols,such as C₁-C₄ monohydric alcohols, C₁-C₄ dihydric alcohols, glycerol andthe like; ethers, such as tetrahydrofuran, diethyl ether,di(n-propyl)ether, diisopropyl ether, diglyme, 1,4-dioxane, ethyleneglycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycoldiethyl ether, propylene glycol monomethyl ether, propylene glycoldimethyl ether and the like; ketones, such as acetone, methyl ethylketone, methyl propyl ketone, methyl(n-butyl)ketone, methyl isobutylketone, methyl amyl ketone, cyclopentanone, cyclohexanone and the like;nitriles, such as acetonitrile, propionitrile, n-butyronitrile,isobutyronitrile and the like; dimethyl sulfoxide, dimethyl sulfone,sulfolane and the like. Of these, particularly preferred are thosesolvents having a hydroxyl group, such as C₁-C₄ monohydric alcohols,C₁-C₄ dihydric alcohols, glycerol, ethylene glycol monomethyl ether andpropylene glycol monomethyl ether. The reason why the use of suchsolvents having a hydroxyl group is preferred is because the use of sucha solvent in the composition of the present invention improves the filmforming properties of the composition, rendering it easy to form a thinfilm having a uniform film thickness.

It is preferred that the amount of the solvent (C) in the composition ofthe present invention is 0.05% by weight or more, based on the weight ofthe composition. If the amount of the solvent (C) is less than 0.05% byweight, based on the weight of the composition, a gelation of thealkoxysilane (A) by the hydrolysis and dehydration-condensation reactionthereof tends not to proceed efficiently, thereby rendering it difficultto produce not only a practically employable silica-organic polymercomposite thin film but also a practically employable porous silica thinfilm.

The composition of the present invention may contain a substance whichis capable of functioning as a catalyst for promoting the hydrolysis anddehydration-condensation reaction of the alkoxysilane (A). Examples ofsuch substances which are capable of functioning as a catalyst includeacids, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoricacid, formic acid, acetic acid, oxalic acid, malonic acid, maleic acid,toluenesulfonic acid and the like; and bases, such as an aqueous ammoniasolution, potassium hydroxide, sodium hydroxide, triethylamine,triethanolamine, pyridine, piperidine, choline and the like. However, ifa base is used as a catalyst, the pore size of the porous silica thinfilm tends to become too large. Therefore, the use of an acid ispreferred. Acids and bases may be used individually or in combination.Further, if desired, the composition may be stepwise treated using anacid and a base. Herein, the term “stepwise treated” means a mode inwhich, for example, the composition is treated first with an acid andthen with a base. Alternatively, the acid and the base may also be usedin the reverse order. In those cases, two different types of catalystsare added to the composition.

When a catalyst is employed, the amount of the catalyst is 1 mole orless, preferably 10⁻¹ mole or less, per mole of the alkoxysilane (A).When the amount of the catalyst is more than 1 mole, per mole of thealkoxysilane (A), the catalyst tends to form a deposit, therebyrendering it difficult to obtain a homogeneous porous silica thin film.

Water is required for the hydrolysis of the alkoxysilane (A) in thepresent invention. The manner of supply of water is not specificallylimited but can be made in any desired manner. For example, when acatalyst is employed, water may be added to the catalyst in advance.When a catalyst is added in an aqueous solution form, the water in theaqueous solution may be used for the hydrolysis of the alkoxysilane (A).Further, when the hydrolysis of alkoxysilane (A) is performed in anatmosphere containing a relatively large amount of steam and the amountof the steam is sufficient to effect the hydrolysis, it is unnecessaryto supply water. The amount of water suitable for the hydrolysis of thealkoxysilane (A) is 10⁴ moles or less, preferably 10 moles or less, permole of the silicon atoms contained in the alkoxysilane (A). When theamount of water used is more than 10⁴ moles, per mole of the siliconatoms contained in the alkoxysilane (A), the homogeneity of thesilica-organic polymer composite thin film tends to become low.

If desired, various additives, such as a photocatalyst generator forimparting a photosensitivity, an agent for improving the adhesion to asubstrate, and a stabilizer for a long-term storage, may be added to thecomposition of the present invention in such an amount as will notimpair the effects of the present invention.

The silica-organic polymer composite thin film can be produced by aprocess comprising:

forming a thin film of the composition obtained by the above-mentionedmanner;

subjecting the thin film to a hydrolysis and dehydration-condensationreaction with respect to the alkoxysilane (A) thereof, to thereby causethe alkoxysilane (A) to be gelled in the thin film; and

removing the solvent (C) remaining in the thin film by drying.

In the present invention, the term “silica” means both SiO₂ and acompound having a structure wherein a hydrocarbon group and a hydrogenatom are bonded to silicon atoms, specifically a structure representedby the following formula;

R′_(x)H_(y)SiO_(z)

wherein R′ represents a C₁-C₆ hydrocarbon group, 0≦x<2, 0≦y<2,0≦(x+y)<2, and 1<z≦2.

The formation of a thin film is performed by coating a substrate withthe composition of the present invention. As a method for forming a thinfilm, any conventional method, such as casting, immersing, spin coatingand the like, can be employed. However, the spin coating method issuitable when the production of the insulating layer is intended in acurrent process for producing a multilayer circuit structure for asemiconductor device. The thickness of the thin film can be controlledwithin the range of from 0.1 μm to 100 μm by varying the viscosity ofthe composition and the revolution rate of the spin coater. When thethickness of the thin film is larger than 100 μm, the thin film tends tosuffer cracking. Generally, when the insulating layer is used in amultilayer circuit structure for a semiconductor device, the suitablethickness of the insulating layer is 0.5 μm to 5 μm.

Examples of substrates include substrates comprised of a single elementsubstance semiconductor, such as silicon or germanium, and substratescomprised of a compound semiconductor, such as gallium-arsenic orindium-antimony. These semiconductor substrates may be used in a formhaving formed thereon a thin film of a substance other than thesubstance used as a material for the substrate. Examples of substancesfor such a thin film formed on a semiconductor substrate include metals,such as aluminum, titanium, chromium, nickel, copper, silver, tantalum,tungsten, osmium, platinum, gold and the like; inorganic compounds, suchas silicon dioxide, fluorinated glass, phosphate glass, borate-phosphateglass, borosilicate glass, polycrystalline silicon, alumina, titania,zirconia, silicon nitride, titanium nitride, tantalum nitride, boronnitride, hydrogen silsesquioxane; and organic polymers, such as methylsilsesquioxane, amorphous carbon, fluorinated amorphous carbon andpolyimide.

Prior to the formation of a thin film of the composition on a substrate,the surface of the substrate may be treated with an agent for improvingthe adhesion to the thin film. As examples of agents for improving theadhesion to the thin film, there can be mentioned substances used as aso-called silane coupling agent or chelate compounds of aluminum.Especially preferred examples of agents for improving the adhesioninclude 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,vinyltrichlorosilane, vinyltriethoxysilane,3-chloropropyltrimethoxysilane, 3-chloropropylmethyldichlorosilane,3-chloropropylmethyldimethoxysilane, 3-chloropropylmethyldiethoxysilane,3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldimethoxysilane,3-methacryloxypropyltrimethoxysilane,3-methacryloxypropylmethyldimethoxysilane, hexamethyldisilazane, (ethylacetoacetato)aluminum diisopropylate, tris(ethyl acetoacetato)aluminum,bis(ethyl acetoacetato)aluminum monoacetylacetonate,tris(acetylacetonato)aluminum and the like. If desired, when the agentfor improving an adhesion to the thin film is applied onto a substrate,other additives may be added to the agent, and the agent may be dilutedwith a solvent. The treatment of the surface of the substrate with theagent for improving an adhesion to the thin film is conducted by a knownmethod.

When alkoxysilane (A) in the thin film which is obtained by theabove-mentioned method is gelled by a hydrolysis anddehydration-condensation reaction, a reaction product having a threedimensional network structure similar to the structure of silicondioxide is obtained.

There is no particular limitation with respect to the temperature forthe hydrolysis and dehydration-condensation reaction of alkoxysilane (A)(hereinbelow, this temperature is-simply referred to as “reactiontemperature”). However, the reaction temperature is usually 0 to 180°C., preferably 30 to 150° C. When the reaction temperature is lower than0° C., the reaction rate becomes small, so that the time required forthe satisfactory gelation of the alkoxysilane (A) becomesdisadvantageously long. On the other hand, when the reaction temperatureis higher than 180° C., formation of large voids tends to occur, so thatthe homogeneity of the below-mentioned silica-organic composite thinfilm is lowered. The time for the hydrolysis anddehydration-condensation reaction of alkoxysilane (A) varies dependingon the temperature of the heat treatment, the amount of the catalyst andthe like. However, usually, the reaction is completed within severalminutes to several days.

In general, the gelation of the alkoxysilane (A) occurs simultaneouslywith the evaporation of at least a part of the solvent (C). However, byusing a solvent having an appropriate boiling point and, if desired, anappropriate type of a catalyst in an appropriate amount, it is possibleto control the rate of the gelation of the alkoxysilane (A) and the rateof the evaporation of the solvent (C).

In many cases, when the solvent (C) is appropriately selected so that atleast a part of the solvent (C) remains in the thin film until thegelation of the alkoxysilane (A) satisfactorily proceeds, favorableresults can be obtained. When the solvent (C) remains in the thin filmat the point in time of completion of the gelation of the alkoxysilane(A), the thin film is subsequently subjected to drying so as to removethe solvent (C) remaining in the thin film. Needless to say, thetemperature for drying varies depending on the type of the solvent (C).Usually, the temperature for drying is 30 to 250 ° C. It is alsoeffective to perform the drying under a reduced pressure. It is alsopreferred that the drying is performed while gradually elevating thetemperature so as to avoid the occurrence of voids and obtain ahomogeneous silica-organic polymer composite thin film.

By the above-mentioned method, a silica-organic polymer composite thinfilm can be obtained. The organic polymer (B) is dispersed in theobtained composite thin film almost in the form of molecular chainswithout suffering aggregation. When the above-mentioned dispersion ofthe molecular chains of the organic polymer (B) in the composite thinfilm is achieved, the composite thin film is transparent to visible rayshaving a wavelength of 0.4 to 0.7 μm.

The thus obtained silica-organic polymer thin film has a low dielectricconstant, as compared to the silicon dioxide obtained using onlyalkoxysilane(s). Further, the thickness of the silica-organic polymerthin film can be rendered satisfactorily large. Therefore, thesilica-organic polymer thin film as such can be used as an insulatinglayer for a multilevel interconnect for a semiconductor device. However,in order to obtain an insulating layer for a multilevel interconnect fora semicondensor device, which has a further lower dielectric constant,it is preferred that this composite thin film is converted to a poroussilica thin film. The composite thin film can be converted to a poroussilica thin film by removing the organic polymer (B) from the compositethin film. If the gelation of the alkoxysilane (A) has satisfactorilyproceeded, when the organic polymer (B) is removed from the compositethin film, the spaces in the composite thin film, which had beenoccupied by the molecular chains of the organic polymer (B), are notcollapsed but left as pores in the porous silica thin film. As a result,a porous silica thin film having a high void ratio and hence a lowdielectric constant can be obtained.

Examples of methods for removing the organic polymer (B) includecalcination by heating, plasma treatment, solvent extraction and thelike. Among these methods, calcination by heating is preferred sincecalcination by heating can be easily performed in the current processfor producing a semiconductor device. When the organic polymer (B) isremoved by calcination, the calcination temperature varies depending onthe type of the organic polymer (B) used. The calcination temperature isusually 300 to 500° C., preferably 350 to 450° C. When the calcinationtemperature is higher than 500° C., the pores of the resultant poroussilica thin film are likely to be collapsed, so that the thickness ofthe thin film is extremely decreased and the dielectric constant of thethin film becomes disadvantageously high. On the other hand, when thecalcination temperature is lower than 300° C., the organic polymer (B)is not satisfactorily decomposed, so that some organic substancesderived from the organic polymer (B) may remain in the resultant poroussilica thin film as impurities, and, hence, it becomes difficult toobtain a porous silica thin film having a low dielectric constant.

The calcination is conducted for 1 minute to 24 hours. When thecalcination time is shorter than 1 minute, the organic polymer (B) isnot satisfactorily decomposed, so that some organic substances derivedfrom the organic polymer (B) may remain in the resultant porous silicathin film as impurities, and, hence, to it becomes difficult to obtain aporous silica thin film having a low dielectric constant. In general,thermal decomposition of the organic polymer (B) is completed within 24hours. Therefore, a long-time calcination for more than 24 hours isuseless.

The calcination can be conducted in an atmosphere of an inert gas, suchas argon, helium and the like, or in an oxidizing atmosphere, such as anatmosphere of an oxygen-containing gas (for example, air and the like).In general, when the calcination is conducted in an oxidizingatmosphere, the calcination temperature tends to be lowered and thecalcination time tends to become short. When the calcination isconducted in an atmosphere of a gas containing ammonia or hydrogen,nitridation or hydrogenation of the porous silica thin film occurs dueto the reaction of the silanol groups remaining in the product obtainedby the hydrolysis and dehydration-condensation reaction of alkoxysilane(A), so that the hygroscopicity of the resultant porous silica thin filmcan be advantageously lowered.

The silica-organic polymer composite thin film and porous silica thinfilm, each of which is obtained from the composition of the presentinvention, can be fabricated into a desired shape by a conventionalmethod used in a current process for producing a semiconductor device.

Surface treatment of the obtained porous silica thin film with asilylating agent is effective for lowering the hygroscopicity of theporous silica thin film and improving the adhesion of the porous silicathin film to other substances. Examples of silylating agents includealkoxysilanes, such as trimethylmethoxysilane, trimethylethoxysilane,dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane,methyltriethoxysilane, dimethylethoxysilane, methyldiethoxysilane,dimethylvinylmethoxysilane, dimethylvinylethoxysilane,diphenyldimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilaneand phenyltriethoxysilane; chlorosilanes, such as trimethylchlorosilane,dimethyldichlorosilane, methyltrichlorosilane, methyldichlorosilane,dimethylchlorosilane, dimethylvinylchlorosilane,methylvinyldichlorosilane, methylchlorodisilane, triphenylchlorosilane,methyldiphenylchlorosilane and diphenyldichlorosilane; and silazanes,such as hexamethyldisilazane, N,N′-bis(trimethylsilyl)urea,N-(trimethylsilyl)acetamide, dimethyl(trimethylsilyl)amine,diethyl(triethylsilyl)amine and trimethylsilylimidazole. Examples ofmethods for the silylation include application of the silylating agentby coating, immersing in the silylating agent or a solution thereof,exposure to the vapor of the silylating agent, and the like.

In a current process for producing a semiconductor device, a siliconoxide insulating layer for a multilevel interconnect for a semiconductordevice is produced by a method comprising dissolving a silicon oxideprecursor in an appropriate solvent to thereby obtain a solution of thesilicon oxide precursor, forming a coating of the obtained solution on asubstrate by spin coating technique or the like, and calcining thecoating at an appropriate temperature. When the alkoxysilane/organicpolymer composition of the present invention {which comprises (A) aspecific alkoxysilane; (B) a specific organic polymer; and (C) a solventfor alkoxysilane (A) and organic polymer (B), wherein solvent (C)comprises at least one organic solvent selected from the groupconsisting of amide linkage-containing organic solvents and esterlinkage-containing organic solvents} is used in place of theabove-mentioned solution of the silicon oxide precursor and subjected toa treatment similar to the above-mentioned current process for producingan insulating thin film, an insulating layer of a multilevelinterconnect for a semiconductor device, which has a low dielectricconstant, can be easily produced.

When the composition of the present invention is used, a silica-organicpolymer composite thin film having a low dielectric constant or a poroussilica thin film having micropores in a high void ratio and hence havinga low dielectric constant can be obtained by a method which can beeasily performed in the conventional process for producing asemiconductor device without any special equipment. Therefore, thecomposition of the present invention is extremely useful as a materialfor an insulating layer for a multilevel interconnect, which has a lowdielectric constant, especially as a material for an insulating layerfor a multilevel interconnect for an LSI.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples, whichshould not be construed as limiting the scope of the present invention.

In the following Examples and Comparative Examples, various propertiesof a silica-organic polymer composite thin film and of a porous silicathin film were evaluated by the following methods.

(1) Measurement of the surface area (N₂ BET): Measurement was performedby means of Nitrogen Adsorption Isotherm Surface Area MeasurementApparatus (manufactured and sold by Shimadzu Corporation, Japan).

(2) Measurement of the film thickness: Measurement was performed bymeans of DEKTAK-II A Model surface roughness measurement apparatus(manufactured and sold by Sloan Technology Corporation, U.S.A).

(3) Measurement of the dielectric constant: Measurement was performed bymeans of HP4280 Model C-V measurement apparatus (manufactured and soldby Hewlett-Packard Company, U.S.A).

(4) Evaluation of the transparency: Evaluation was made by the followingmethod. A silica-organic polymer composite thin film is cut into a slicehaving a thickness of 1 mm. The slice was placed on a plate carrying ablack character having a size of 3 mm×3 mm so that the character iscovered by the slice. The character is then visually observed throughthe slice. If the character is legible through the slice, the slice isevaluated as being transparent.

The number average molecular weight (Mn) of an organic polymer usedherein was measured by gel permeation chromatography (GPC) usingtetrahydrofuran as an eluent and using a calibration curve obtained withrespect to standard monodispersed polystyrene systems.

The following abbreviations are used in Tables 1 to 7 showing the dataof Examples and Comparative Examples.

TEOS: tetraethoxysilane,

MTES: methyltriethoxysilane,

TMOS: tetramethoxysilane,

MTMS: methyltrimethoxysilane,

PEG: polyethylene glycol,

PCL: polycaprolactone,

PC: poly(pentamethylene-hexamethylene carbonate),

PVEE: polyvinyl ethyl ether,

PVdF: polyvinylidene fluoride,

NMP: N-methylpyrrolidone,

DMF: N,N-dimethylformamide,

EA: ethyl acetate,

EtOH: ethanol, and

MeOH: methanol

EXAMPLE 1

1.2 g of tetraethoxysilane and 0.34 g of polyethylene glycol (numberaverage molecular weight: 20,000) were dissolved in 2.0 g ofN-methylpyrrolidone. Then, added thereto were 0.30 g of water and 0.15 gof 0.10 N nitric acid, and the resultant solution was stirred for 2hours at room temperature. This solution was cast onto apolytetrafluoroethylene watch-glass and allowed to stand for 1 hour at120° C. to thereby cause the tetraethoxysilane to be gelled. Theresultant gel was dried in vacuum at 180° C., to thereby obtain asilica-organic polymer composite thin film. The obtained composite thinfilm was transparent.

EXAMPLES 2 TO 14

Substantially the same procedure as in Example 1 was repeated, exceptthat the types of the alkoxysilane, the organic polymer and the solventwere varied. The types and amounts of alkoxysilanes, organic polymersand solvents which were employed and the obtained results are shown inTable 1. The term “weight of gel” indicated in Table 1 means the weightof a hydrolysis and dehydration-condensation reaction product of analkoxysilane employed, as determined by calculation, based on theassumption that the entire amount of the alkoxysilane undergoes ahydrolysis and dehydration-condensation reaction.

All of the obtained silica-organic polymer thin films were transparent.

TABLE 1 Amount of alkoxy- Weight Molecular Amount of Example Alkoxy-silane of gel weight of polymer Appearance No. silane (g) (g) Polymerpolymer (g) Solvent of gel 1 TEOS 1.2 0.34 PEG 20000 0.34 NMPTransparent 2 TEOS 1.2 0.34 PEG 20000 0.68 NMP Transparent 3 MTES 0.90.34 PEG 20000 0.34 DMF Transparent 4 MTES 0.9 0.34 PEG 600 0.51 NMPTransparent 5 MTMS 0.7 0.34 PEG 20000 0.34 NMP Transparent 6 MTMS 0.70.34 PEG 1000 0.68 EA Transparent 7 TMOS + MTMS 0.8 0.34 PEG 2000 0.51EA Transparent (1/1) 8 TEOS 1.2 0.34 PCL 600 0.34 DMF Transparent 9 MTMS0.7 0.34 PCL 600 0.34 DMF Transparent 10 MTMS 0.7 0.34 PC 20000 0.34 NMPTransparent 11 TEOS 1.2 0.34 PEG 20000 0.68 NMP + EtOH Transparent (2/8)12 MTES 0.9 0.34 PEG 20000 0.85 NMP + EtOH Transparent (2/8) 13 MTMS 0.70.34 PEG 600 1.05 DMF + EG Transparent (5/5) 14 MTMS 0.7 0.34 PEG 200000.34 NMP + MeOH Transparent (3/7)

Comparative Examples 1 to 4

Substantially the same procedure as in Example 1 was repeated, exceptthat polyvinyl ethyl ether (PVEE) and polyvinylidene fluoride (PVdF)were used as organic polymers. The results are shown in Table 2. Atransparent and homogeneous gel could not be obtained in ComparativeExamples 1 to 4.

TABLE 2 Amount of alkoxy- Weight Molecular Amount of Compara. Alkoxy-silane of gel weight of polymer Ex. No. silane (g) (g) Polymer polymer(g) Solvent Gelation 1 TEOS 1.2 0.34 PVEE 3800 0.34 NMP Homogeneousgelation did not occur. 2 TEOS 1.2 0.34 PVdF 71000 0.34 DMF Opaque gelwas formed. 3 MTMS 0.7 0.34 PVdF 71000 0.34 NMP Opaque gel was formed. 4MTMS 0.7 0.34 PVdF 71000 0.34 EA Opaque gel was formed.

EXAMPLES 15 TO 26

0.17 g of one polymer selected from the group consisting of polyethyleneglycol (number average molecular weight: 20,000), polycaprolactone(number average molecular weight: 600) andpolypentamethylene-hexamethylene carbonate (number average molecularweight: 2,000) was dissolved in 1.5 g of one solvent selected from thegroup consisting of N,N-dimethylformamide (DMF), N-methylpyrrolidone(NMP), ethyl acetate and a mixed solvent (weight ratio: 6/4) oftetrahydrofuran (THF) and DMF. Then, added thereto were 0.60 g oftetraethoxysilane (corresponding to 0.17 g in terms of SiO₂) and 0.15 gof 0.1 N hydrochloric acid, and the resultant solution was stirred for 1hour at room temperature. When 0.5 g of 0.1 N aqueous ammonia solutionwas added to this solution, tetraethoxysilane gelled rapidly and thewhole of the solution became a jelly-like product.

As shown in Table 3, all of the obtained jelly-like products werecolorless and transparent.

TABLE 3 Appearance of gel Example Ethyl THF + DMF No. Polymer DMF NMPacetate (6/4) 15-18 PEG T T T T 19-22 PCL T T T T 23-26 PC T T T T T:Transparent, O: Opaque

Comparative Examples 5 to 7

Substantially the same procedures as in Examples 15 to 26 were repeated,except that acetonitrile was used as the solvent. As shown in Table 4,all of the obtained jelly-like products were white opaque.

TABLE 4 Appearance Compara. of gel Ex. No. Polymer Acetonitrile 5 PEG O6 PCL O 7 PC O T: Transparent, O: Opaque

EXAMPLE 27

0.43 g of ETHYL SILICATE 40 (manufactured and sold by Colcoat KabushikiKaisha, Japan) and 0.17 g of polypropylene glycol (number averagemolecular weight: 4,000) were dissolved in a mixed solvent of 1.2 g ofdimethylformamide and 0.8 g of ethanol. Then, added thereto was 0.2 g of0.1 N aqueous ammonia solution. The resultant solution was cast onto apetri dish so as to form a thin film thereon. Then, the petri dish wassealedly covered and allowed to stand overnight at room temperature tothereby cause ETHYL SILICATE 40 to be gelled. Subsequently, thetemperature of the atmosphere surrounding the thin film was graduallyelevated from 60° C. to 120° C. and then the pressure of the atmospheresurrounding the thin film was reduced to vacuum while maintaining thetemperature at 120° C., thereby drying the thin film, thus obtaining atransparent silica-organic polymer composite thin film having athickness of 1.3 mm. The obtained composite thin film was calcined for 2hours at 450° C. in air, thereby removing the organic polymer to obtaina porous silica thin film. The specific surface area of the obtainedporous silica thin film was measured by nitrogen adsorption isothermmethod, and was found to be 990 m²/g. This value indicates that the porediameter of the obtained porous silica thin film is small.

Comparative Example 8

0.43 g of ETHYL SILICATE 40 (manufactured and sold by Colcoat KabushikiKaisha, Japan) and 0.17 g of polystyrene were dissolved in 2.0 g ofmethyl ethyl ketone. Further, added thereto was 0.2 g of 0.1 N aqueousammonia solution. The resultant solution was cast onto a petri dish tothereby form a thin film. Then, the petri dish was sealedly covered andallowed to stand overnight at room temperature to thereby cause ETHYLSILICATE 40 to be gelled. Subsequently, the temperature of theatmosphere surrounding the thin film was gradually elevated from 60 to120° C. and then the pressure of the atmosphere surrounding the thinfilm was reduced to vacuum while maintaining the temperature at 120° C.,thereby drying the thin film, thus obtaining an opaque silica-organicpolymer composite thin film. The obtained composite thin film wascalcined for 2 hours at 450° C. in air, thereby removing the organicpolymer to obtain a porous silica thin film. The specific surface areaof the obtained porous silica thin film was measured using 0.13 g of theporous silica thin film, and found to be as small as 1 m²/g or less.This indicates that the pore diameter of the obtained porous silica thinfilm is large.

EXAMPLE 28

1.2 g of tetraethoxysilane (TEOS) and 0.17 g of polyethylene glycol(number average molecular weight: 20,000) were dissolved in a mixedsolvent (weight ratio: 2/1) of N,N′-dimethylimidazolidinone andpropylene glycol methyl ether acetate. Then, added thereto were 0.5 g ofwater and 0.15 g of 0.1 N hydrochrolic acid, and the resultant solutionwas stirred for 4 hours.

A silicon wafer having a titanium nitride thin film thereon was coatedwith the above solution by spin coating (revolution rate: 1,500 rpm) tothereby form a thin film. The formed thin film was heated for 1 hour at120° C. so as to effect a gelation of the tetraalkoxysilane and removethe solvent, thereby obtaining a silica-organic polymer composite thinfilm.

The obtained composite thin film was calcined for 1 hour at 450° C. inan atmosphere of nitrogen gas to thereby remove the organic polymer,thereby obtaining a porous silica thin film. The obtained porous silicathin film was placed in a pressure vessel, and the internal pressure ofthe pressure vessel was reduced to vacuum. Then, a vapor ofhexamethyldisilazane was introduced into the pressure vessel at roomtemperature, to thereby modify the pore surfaces with trimethylsilylgroups so as to render the pore surfaces hydrophobic. The upper surfaceof this thin film was coated with aluminum by vacuum deposition througha SUS mask to thereby form an electrode having a diameter of 1.7 mm.Using the thus obtained electrode-carrying porous silica thin film, thedielectric constant of the porous silica thin film was measured at 1MHz. The dielectric constant of the porous silica thin film was found tobe 3.5, which is remarkably lower than the dielectric constant (4.5) ofSiO₂.

EXAMPLES 29 TO 32

Substantially the same procedure as in Example 28 was repeated, exceptthat the amount of polyethylene glycol was varied. The results of thedielectric constant measurement are shown in Table 5. As shown in Table5, all of the obtained porous silica thin films exhibited low dielectricconstant values.

TABLE 5 Thickness of Thickness of Ratio of composite film after decreaseDielectric Example Alkoxy- Polymer/silica film calcination in thick-constant No. silane Polymer weight ratio (μm) (μm) ness (1 MHz) 28 TEOSPEG 0.5 0.65 0.48 26% 3.5 29 TEOS PEG 1.0 1.19 0.83 30% 2.7 30 TEOS PEG1.5 0.93 0.63 32% 2.5 31 TEOS PEG 2.0 1.02 0.64 37% 2.2 32 TEOS PEG 3.01.09 0.71 35% 1.7

EXAMPLE 33

0.70 g of methyltrimethoxysilane (MTMS) and 0.17 g of polyethyleneglycol (number average molecular weight: 20,000) were dissolved in amixed solvent (weight ratio: 2/1/4) of N-methylpyrrolidone, propyleneglycol methyl ether acetate and methanol. Then, added thereto were 0.30g of water and 0.15 g of 0.1 N nitric acid, and the resultant solutionwas stirred for 3 hours.

A silicon wafer having a titanium nitride thin film thereon was coatedwith the above solution by spin coating (revolution rate: 1,500 rpm) tothereby form a thin film. The formed thin film was heated for 1 hour at120° C. so as to effect a gelation of MTMS and remove the solvent,thereby obtaining a silica-organic polymer composite thin film.

The obtained composite thin film was calcined for 1 hour at 450° C. inan atmosphere of nitrogen gas to thereby remove the organic polymer,thereby obtaining a porous silica thin film. The upper surface of thisthin film was coated with aluminum by vacuum deposition through a SUSmask to thereby form an electrode having a diameter of 1.7 mm. Using thethus obtained electrode-carrying porous silica thin film, the dielectricconstant of the porous silica thin film was measured at 1 MHz. Thedielectric constant of the porous silica thin-film was found to be 2.8,which is lower than the dielectric constant (3.1) of CH₃SiO_(1.5).

EXAMPLES 34 TO 36

Substantially the same procedure as in Example 33 was repeated, exceptthat the amount of polyethylene glycol was varied. The results of thedielectric constant measurement are shown in Table 6. As shown in Table6, all of the obtained porous silica thin films exhibited low dielectricconstant values.

TABLE 6 Thickness of Thickness of Ratio of composite film after decreaseDielectric Example Alkoxy- Polymer/silica film calcination in thick-constant No. silane Polymer weight ratio (μm) (μm) ness (1 MHz) 33 MTMSPEG 0.5 1.03 0.74 28% 2.8 34 MTMS PEG 1.0 0.94 0.63 33% 2.4 35 MTMS PEG1.5 1.06 0.67 37% 2.1 36 MTMS PEG 3.5 1.00 0.64 36% 1.6

Comparative Example 9

0.70 g of methyltrimethoxysilane (MTMS) and 0.17 g of polyethyleneglycol (number average molecular weight: 20,000) were dissolved inmethanol. Then, added thereto were 0.30 g of water and 0.15 g of 0.1 Nnitric acid, and the resultant solution was stirred for 2 hours.

A silicon wafer was coated with the above solution by spin coating(revolution rate: 1,500 rpm) to thereby form a thin film. The formedthin film was heated for 1 hour at 120° C. so as to effect a gelation ofMTMS and remove the solvent, thereby obtaining a silica-organic polymercomposite thin film having a thickness of 0.87 μm.

The obtained composite thin film was calcined for 1 hour at 450° C. inan atmosphere of nitrogen gas to thereby remove the organic polymer,thereby obtaining a porous silica thin film. The thickness of the poroussilica thin film was 0.45 μm, indicating that the calcination caused athickness decrease as large as 48%, based on the thickness of thesilica-organic polymer composite thin film. It is presumed that poreswhich should have been formed when the organic polymer was removed bycalcination were collapsed.

Comparative Examples 10 and 11

Substantially the same procedure as in Comparative Example 9 wasrepeated, except that the amount of polyethylene glycol was varied. Theresults of the measurement of the ratio of decrease in the filmthickness are shown in Table 7. As shown in Table 7, the calcinationcaused a marked decrease in the film thickness in Comparatives Examples10 and 11.

TABLE 7 Thickness Thickness Polymer/ of of Ratio of Com- silicacomposite film after decrease para. Alkoxy- Poly- weight filmcalcination in thick- Ex. No. silane mer ratio (μm) (μm) ness  9 MTMSPEG 0.5 0.87 0.45 48% 10 MTMS PEG 1.0 0.36 0.14 61% 11 MTMS PEG 1.5 1.140.47 59%

EXAMPLE 37

0.6 g of methyltrimethoxysilane and 0.1 g of polysebacic anhydride(number average molecular weight: 1,900) were dissolved in 1.0 g ofN,N-dimethylformamide. Then, added thereto were 0.05 g of water and 0.1g of 0.1 N hydrochloric acid, and the resultant solution was stirred for1 hour at room temperature. This solution was cast onto apolytetrafluoroethylene watch glass to thereby form a thin film, and theformed thin film was allowed to stand for 1 hour at 100° C. to therebycause the methyltrimethoxysilane to be gelled. Then, the thin film wasdried in vacuum at 180° C., thereby obtaining a silica-organic polymercomposite thin film. The dried composite thin film was transparent.

INDUSTRIAL APPLICABILITY

Both of the silica-organic polymer composite thin film (which isproduced by a process comprising: forming a thin film of thealkoxysilane/organic polymer composition of the present invention;subjecting the thin film to a hydrolysis and dehydration-condensationreaction with respect to the alkoxysilane thereof, to thereby cause thealkoxysilane to be gelled in the thin film; and removing the solventremaining in the thin film by drying) and the porous silica thin film(which is obtained by removing the organic polymer from thesilica-organic polymer composite thin film) have advantages not only inthat these thin films have a low dielectric constant suitable forinsulating layers for a multilevel interconnect for asemiconductor-device, but also in that these thin films can be producedby a method which can be easily performed in the current process forproducing a semiconductor device. Therefore, the alkoxysilane/organicpolymer composition of the present invention for use in producing aninsulating thin film can be very advantageously used for producing aninsulating layer for a multilevel interconnect for a semiconductordevice, such as an LSI.

What is claimed is:
 1. An alkoxysilane/organic polymer composition foruse in producing an insulating thin film, comprising: (A) at least onealkoxysilane selected from the group consisting of (1)tetraalkoxysilanes, (2) trialkoxysilanes, (3) dialkoxysilanes, (4)monoalkoxysilanes and (5) trialkoxysilane dimers, respectively,represented by the following formulae (1), (2), (3), (4) and (5):Si(OR)₄  (1), R¹Si(OR)₃  (2), R¹R²Si(OR)₂  (3), R¹R²R³SiOR  (4), and(RO)₃Si—R⁴—Si(OR)₃  (5), wherein each R independently represents astraight chain or branched alkyl group having 1 to 6 carbon atoms, eachof R¹, R² and R³ independently represents a hydrogen atom or amonovalent hydrocarbon group having 1 to 6 carbon atoms, and R⁴represents a divalent hydrocarbon group having 1 to 6 carbon atoms, andwherein, when said alkoxysilane (A) is at least one first alkoxysilaneselected from the group consisting of said alkoxysilanes (3) and (4),said first alkoxysilane is used in combination with at least one secondalkoxysilane selected from the group consisting of said alkoxysilanes(1), (2) and (5); (B) at least one organic polymer having a main chainmainly comprising at least one polymer chain selected from the groupconsisting of an, aliphatic polyether chain having ethergroup-containing recurring units having 2 to 12 carbon atoms, analiphatic polycarbonate chain having carbonate group-containingrecurring units having 2 to 12 carbon atoms and an aliphaticpolyanhydride chain having anhydride group-containing recurring unitshaving 2 to 12 carbon atoms; (C) a solvent for said alkoxysilane (A) andsaid organic polymer (B), wherein said solvent (C) comprises at leastone organic solvent selected from the group consisting of amidelinkage-containing organic solvents and ester linkage-containing organicsolvents; and (D) at least one acid capable of functioning as a catalystfor promoting a hydrolysis and dehydration-condensation reaction of saidalkoxysilane (A), wherein said acid is used in an amount of 1 mole orless, per mole of said alkoxysilane (A), and wherein at least a part ofsaid alkoxysilane (A), which is at least one alkoxysilane selected fromthe group consisting of said alkoxysilanes (1) to (5), is optionally inat least one form selected from the group consisting of an oligomer formand an at least partially hydrolyzed form.
 2. The composition accordingto claim 1, wherein said alkoxysilane (A) is a mixture of at least onetetraalkoxysilane (1) and at least one alkoxysilane selected from thegroup consisting of said alkoxysilanes (2) to (5).
 3. The compositionaccording to claim 1, wherein said alkoxysilane (A) is at least onetrialkoxysilane (2), or a mixture of at least one trialkoxysilane (2)and at least one alkoxysilane selected from the group consisting of saidalkoxysilanes (1) and (3) to (5).
 4. The composition according claim 1,wherein said solvent (C) further comprises at least one alcohol.
 5. Thecomposition according to claim 1, wherein said organic polymer (B) is analiphatic polyether comprising a polyalkylene glycol having C₂-C₁₂ ethergroup-containing recurring units and having a number average molecularweight of from 200 to 1,000,000.
 6. The composition according to claim1, wherein said organic polymer (B) is present in an amount of from 0.1to 10 in terms of a weight ratio relative to the amount of a productobtained by subjecting the entire amount of said alkoxysilane (A) to ahydrolysis and dehydration-condensation reaction.
 7. A silica-organicpolymer composite thin film, which is produced by a process comprising:forming a thin film of the composition of claim 1; subjecting said thinfilm to a hydrolysis and dehydration-condensation reaction with respectto said alkoxysilane (A) thereof, to thereby cause said alkoxysilane (A)to be gelled in said thin film, wherein said organic polymer (B) isdispersed in said thin film substantially in the form of moleculerchains; and removing said solvent (C) remaining in said thin film bydrying.
 8. The silica-organic polymer composite thin film according toclaim 7, which has a thickness of from 0.1 to 100 μm.
 9. Thesilica-organic polymer composite thin film according to claim 7, whichis transparent to visible rays having a wavelength of from 0.4 to 0.7μm.
 10. A multilevel interconnect comprising a plurality of insulatinglayers and circuits formed on said insulating layers, wherein at leastone layer of said insulating layers comprises the silica-organic polymercomposite thin film of claim
 7. 11. A semiconductor device comprisingthe multilevel interconnect of claim
 10. 12. The silica-organic polymercomposite thin film according to claim 7, which is for use as at leastone layer of a plurality of insulating layers for a multilevelinterconnect, wherein said interconnect comprises said plurality ofinsulating layers and circuits formed on said insulating layers.
 13. Aprocess for producing a porous silica thin film, comprising removing theorganic polymer from the silica-organic polymer composite thin film ofclaim 7 by calcining said composite thin film at a temperature of nothigher than 450° C. in an inert gas and wherein, when the alkoxysilane(A) is a tetraalkoxysilane (1), treating a pore surface of said poroussilica thin film with a silylating agent.
 14. The process according toclaim 13, wherein said porous silica thin film has an average porediameter of from 1 to 500 nm.